1. Field of the Invention
The Invention is an apparatus for determining and adjusting the angle of the spindle of a machine tool with respect to the working holding surface of the machine tool. The Invention is particularly useful for squaring the spindle of a manual milling machine with respect to the table to which a work piece is to be attached.
2. Description of the Prior Art
Perpendicularity of the tool holder to the work holding surface must be established and quantifiably measured prior to setting up a manually operated spindle-type machine tool. If the spindle is not square to the table, the quality of any work performed using the machine tool may be severely compromised and may cause the resulting product to be rejected.
Establishing perpendicularity of a machine tool spindle to the workholding surface historically has been accomplished manually using labor-intensive procedures. Spindle machine tools generally have two separate angle adjusting mechanisms corresponding to angle adjustments in an “X” direction and in a “Y” direction. The angle of the spindle to the work holding surface generally is separately checked and set for each of the ‘X’ and ‘Y’ directions. U.S. Pat. No. 5,253,425 to Wozniak on Oct. 19, 1993 describes the usual prior art practice. In the prior art practice, one leg of an L-shaped member is affixed to the spindle of the machine tool. A precision dial indicator is attached to the other leg of the L-shaped member.
To check whether the spindle of a machine tool is square to the table with respect to the “X” direction using the prior art method, the operator first orients the L-shaped member in the ‘X’ direction and advances the spindle until the measuring tip of the dial indicator is in contact with the table. The operator reads the gauge, rotates the spindle by 180 degrees, and reads the dial indicator again. The generally accepted rule of thumb is that the difference between the two dial indicator readings should be within 0.0005 inches in 6 inches (0.013 mm in 15.24 cm) of separation between the locations of the two readings. If, for example, the indicator tip describes a circle twelve inches in diameter on the table and if the dial indicator reading varies by more that 0.001 inches along the circumference of the circle, the spindle is not adequately square with respect to the table. The operator will adjust the angle between the spindle and the table in the ‘X’ direction and repeat the measurement process until the spindle is adequately square to the table in the ‘X’ direction. The operator then repeats the process for the ‘Y’ direction.
Using the prior art method, the spindle must be rotated 180 degrees for each measurement and each measurement requires the dial indicator to be read twice. The requirement to rotate the spindle adds to the difficulty of the method and to the discomfort of the machinist, since the dial indicator generally has only one orientation and the machinist is required to change his or her position to read the dial indicator.
The design of manually operated spindle machines such as milling machines also complicates the process of squaring the spindle. These machines have an “off-center” pivot in the ‘Y’ direction making it troublesome for even an experienced machinist to square since it is difficult to judge the amount of adjustment required to bring the spindle of the machine into a perpendicular position. Frequent and time consuming adjustments are required since even the slightest movement may extrapolate into major misalignments because of the off-center nature of the machine tool's pivot.
Another variable is the amount of play in the gears of the machine tool's spindle head. Since these machine tools have useful lives of well over ten years, normal usage causes the gears to wear. While this may not compromise the performance of the machine once it is properly squared and set up, it does complicate the process of squaring the spindle head. The process of squaring the head of the machine tool can become more an intuitive art than a mechanical one, with the machinist often guessing at the amount of alignment necessary to accommodate the unknown level of play in the gears.